1. Field of the Invention
Microscope slides having marking surfaces adapted for marking by pen, pencil or other marking means.
2. Description of the Prior Art
The following list of the U.S. Pat. Nos. comprises the closest prior art known to applicant:
______________________________________ 3,705,050 Smith 4,087,154 Menzel 4,290,533 Rupp et al. 4,481,246 Melisz et al 4,624,882 Melisz et al 4,679,914 Rosenberg ______________________________________
The problem with the epoxy resin type of marking surface, as exemplified by the above-cited Melisz et al. and Rosenberg patents, is that it is not permanently secured to the glass slide. This is equally true of polytetrafluoroethylene coatings that are similarly used as marking surfaces on microscope slides. In both cases, the coatings are vulnerable to chemical or mechanical factors that may detach the coatings from the slides. Additionally, the markings on such marking surfaces may in some cases rub off or erode, preventing their use as permanent records. Moreover, specimens on the slides, e.g., blood smears, may be subject to contamination from dislodged particles of the epoxy resin.
Conventional microscope slide marking surfaces that are permanent ("frosted" marking surfaces) are those formed by sandblasting, acid etching, mechanical abrading, or other surface roughening methods. Such frosted marking surfaces are formed in the glass itself and, consequently are permanently incorporated therein. But they have disadvantages that may outweigh the advantage of their permanence. Thus, they do not provide good writing surfaces and they require opaque backgrounds for visual contrast. Such backgrounds take the form of opaque coatings applied to the reverse side of the slides behind the frosted marking surfaces. The problem of permanence is thereby transferred from the marking surfaces to the background coatings.
The background coatings add the economic disadvantage of an additional material and an additional manufacturing operation that provide no useful function except to improve the functioning of the frosted marking surfaces.
The closest of the above-cited patent art is the Smith U.S. Pat. No. 3,705,050. Smith discloses a method of producing a vitreous enamel marking surface on laboratory glassware "including beakers, flasks, test tubes, culture tubes, Petri dishes, etc." (column 1, lines 34-35). It is noted that these are all curved shapes and that glass distortion is no serious problem with respect to laboratory glassware of the kind specified. But glass distortion is impermissible in microscope slides.
Specifically, the Smith patent is concerned with high annealing temperature glass (borosilicate) and high firing temperature vitreous enamels. The borosilicate glass in Smith's examples has an annealing temperature range of 1030-1050 degrees F. (column 5, lines 29-37). The vitreous enamels mentioned have firing temperatures ranging upwardly from 900 degrees F. (column 5, lines 38-40). The vitreous enamels are fused onto the borosilicate surface in an annealing lehr maintained at a temperature range of about 1030 to 1050 degrees F. (column 4, lines 72-75), the annealing temperature range of the borosilicate glass. A microscope slide, exposed to this temperature range, would change shape.
Smith relies on polytetrafluoroethylene (sold under the duPont trademark Teflon) for the formation of a marking surface capable of accepting pencil and other markings. When the vitreous enamel is softened and fused onto the borosilicate glass the Teflon decomposes, yielding a gas that passes through the vitreous enamel, producing crevices, pinholes and protuberances that provide a roughened marking surface (column 5, lines 1-5). None of this is involved in the present invention.